The present invention relates to a filter, especially for separating fibers from back water in the wood pulp industry, comprising a filter surface which can be moved down into and up from the liquid to be filtered which is contained in a vessel, with said filter surface being constituted by the peripheral surface of a plurality of longitudinal, hollow, horizontal filter elements which are arranged in a ring, a reduced pressure being maintained on the side of the filter surface opposite the liquid compared with the static pressure of the liquid in the vessel, and means for removing the solids deposited on the filter surface when the surface is above the liquid in the vessel.
The filter is especially intended for the wood pulp industry, primarily for filtering of back water for recovering fibers and purifying the back water. However, it may also be used for thickening of pulp etc. Outside the wood pulp industry, the filter may be used e.g. as clean water filter and for recovery, purification and thickening of screenable suspensions in general.